Astronomy Hacks

Protect Your Night Vision from Local Lights

Stay dark adapted and keep stray light from the eyepiece (and keep your ears warm).

Night vision is all-important when you observe DSOs. For those fortunate enough to have access to a truly dark observing site, it’s not difficult to preserve night vision using standard methods—red LED flashlight, covering your notebook computer screen with red film [Hack #44], and so on. But for many astronomers, the only sites within easy driving distance are, at best, semi-dark. The problem with these sites is often not so much general light pollution as local light pollution—the presence of streetlights and other nearby bright light sources.

For example, our regular “dark” observing site routinely offers mag 5.5+ skies, and on good nights mag 6.0 or better [Hack #13]. In terms of general light pollution, that’s a respectable DSO observing site, at least by Eastern U.S. standards. Unfortunately, there are half a dozen mercury-vapor lights within a few hundred yards of the site. Their combined light makes it impossible to become fully dark adapted. In fact, it’s bright enough to read a newspaper on the observing pad, literally. Because the site is on private property, it is impossible to install permanent screens against the local light pollution. Portable screens are impractical for various reasons.

Fortunately, there is a cheap, easy solution to such local light pollution problems, as long as you don’t mind looking like a complete idiot. ...